This invention relates in general to the preparation of briquettes primarily for the metallurgical furnace use and in particular, to a new and useful method of producing hot briquettes in a plurality of heating stages.
In a prior art method, known as the ANCIT method and disclosed in West German patent 19 15 905, two flash reactors are series connected in the gas flow path, so that initially, in a first flash reactor and by means of the same gas stream which is used in the next stage, the pneumatically introduced inert component is heated up to about 600.degree. C., and may be simultaneously degassed. After separating this component from the gas in a following cyclone, the same gas is directed into a second flash reactor where it is used to heat the, also pneumatically introduced, binder component to a temperature which is lower than that of the inert component at the outlet of the first cyclone. In methods of this kind, after a separation in a following cyclone, a lean gas of low calorific value and loaded with residual dust is obtained which still has a sensibly high temperature and is then cooled and purified in a wet scrubber to be further used.
With such a method, the sensible thermal energy absorbed by the water can hardly be further utilized. Also, the residual dust present in the gas is necessarily obtained in the form of mud requiring a troublesome further treatment.
To enlarge the coal basis for this method, there is known to use as the inert component poorly caking, more volatile coals after a special thermal treatment (see Stahl and Eisen 92,1972, No. 21, page 1041). The coal is subjected to this preliminary treatment in a short flash reactor and at relatively low temperatures. The coal is then separated from the waste gas in a cyclone, cooled with water and recycled to the coal charging bins. Consequently, after this advance treatment, the more volatile coal, having the temperature of the ambience, must again be heated up. This requies a great amount of additional energy to be supplied, and again residual dust is obtained in the form of mud.
In a modified method of this kind, a fluidized-bed drier may be substituted for the flash reactor.
According to another prior art method, known as the BFL hot briquetting method and described, for example, in the book "Rohstoff Kohle" published by Verlag Chemie Weinheim 1978, pages 276 to 277, coal carbonizing at low temperatures and binder coal are dried separately in a flash drier and the binder coal is comminuted to particles smaller than one millimeter. After drying, the low-temperature coal is heated up in a mixer with hot low-temperature coke (about 800.degree. C.) and degassed. After degassing, the low-temperature coke is directed for further heating into an uptake and then, through a collecting bin, to the hot briquetting process proper, where it is pressed, together with the binder, to briquettes. So, in this method, the coal components are dried and heated separately, and a separate metering of gas and coal amounts is needed for each of the stages. Under elevated-temperature conditions, this is very expensive.